1. Field of the Invention
This invention relates generally to the manufacture of silicon integrated circuits (ICs). More specifically, the present invention relates to integrated circuits utilizing an electrical interconnect system in multilevel conductor-type integrated circuits of high component density and the processes for making the same.
2. State of the Art
In recent years with increasing component density of very large scale integrated circuits, it has become necessary to develop multilevel conductor technologies to provide the required number of electrical interconnects between both active and passive devices fabricated on silicon substrates using state of the art planar processing. These multilevel conductor technologies are also alternatively referred to as multilevel metal (MLM) processing. But as used herein, multilevel conductor (MLC) processing is generic to either metal deposition, polycrystalline silicon deposition, or polysilicon deposition used in the formation of conductive interconnecting paths at different levels or planes formed on an integrated circuit substrate, such levels or planes containing previously formed active and passive devices located therein.
As generally understood in the art and as used herein, a “level” including a conductor or metallization is added atop a semiconductor substrate by growing or depositing an insulating layer, such as silicon dioxide or silicon nitride, over a previously formed underlayer of metal and forming an opening or “via” in this insulating layer for receiving a conductor or metallization to extend therethrough from another conductor or metallization subsequently formed as an upper layer deposited on the surface of the insulating layer. Thus, the mere addition of a single “level” of conductor over a previously formed conductive pattern will include the process steps of (1) the formation of an insulating layer, (2) the formation of a photoresist etch mask on the surface of the insulating layer, (3) the exposure of the etch mask to a selected etchant to create a via in the insulating layer, (4) the removal of the photoresist etch mask, and (5) deposition of an additional layer of metallization or polysilicon in order to provide an electrical interconnect through the previously formed via in the dielectric layer and conductor connected thereto located on the insulating layer.
A number of prior art electrical interconnect systems and processes for the formation thereof have been used in the integrated circuit art, but none such as the electrical interconnect systems of the present invention. For example, U.S. Pat. No. 5,001,079 discloses a method of manufacturing a semiconductor device by forming insulating side walls with voids below overhangs. This method illustrates insulating material layers of silicon oxide, silicon nitride or silicon oxynitride which are deposited by plasma enhanced chemical vapor deposition (CVD), a process known in the art, for the formation of overhanging portions thereof having voids thereinbetween. Such voids are subsequently etched to expose gently sloping portions for further insulation to be added therein.
U.S. Pat. No. 5,278,103 illustrates a method for the controlled formation of voids in doped glass dielectric films wherein the doped glass may include boron phosphorous silicate glass (BPSG) deposited in predetermined thicknesses. BPSG is used for its dielectric properties, its melting point, and for deposition by CVD processes. The controlled formation of voids in the BPSG is used to minimize the effect of parasitic capacitance between conductors located therein.
U.S. Pat. No. 5,166,101 illustrates another method for forming a BPSG layer on a semiconductor wafer using predetermined CVD deposition and plasma-assisted CVD deposition processes to form void-free BPSG layers over stepped surfaces of a semiconductor wafer.
As current semiconductor device performance requirements continue to increase component packing densities of the semiconductor device, this, in turn, increases the complexity and cost of multilevel conductor formation processes requiring further levels of conductors to multilevel conductor integrated circuits. This typically results in lower wafer processing yields, affects semiconductor device reliability, and increases production costs for such semiconductor devices.
What is needed and not illustrated in the prior art described herein are multilevel conductor interconnections and processes for the manufacture thereof in integrated circuit semiconductor devices wherein the electrical interconnections and the density thereof is increased without the addition of another “level” of circuitry for conductors or metallization to the semiconductor device. This increased density of multilevel conductor interconnections without the addition of at least one additional “level” further requires the use of areas of the integrated circuit semiconductor device not presently used for electrical interconnection, requires the use of improved oxide formation and conductor formation processes for maximizing component packing density on each layer of the semiconductor device, and requires minimizing the number of individual process steps for manufacturing. The present invention described hereinafter is directed to such requirements while allowing for the substantially simultaneous formation of electrical interconnections.